There are two traditional methods for making monitoring patterns. One method is based on the well known in-line monitoring pattern and the other method is based on the well known unit device monitoring pattern. Both of these known methods are generally used to confirm critical dimensions (hereinafter referred to as “CD”) and depth.
In a method for in-line monitoring pattern, as described in Korean Patent Registration No. 0301040, electronic beams are applied to a semiconductor substrate having an open pad composed of an impurities-doped poly-silicon layer formed in an in-line during the fabrication of semiconductor device. In response to the application of the electronic beams, the secondary electrons emitted from the pad are imaged as black or white.
A conventional method for measuring the depth of shallow trench isolation (STI) is disclosed in Korean Patent Publication No. 2001-0066143. A trench and an insulating layer respectively having a length of 0.4 micrometer are alternately provided to form a pattern in the shape of a lattice. An indicating value of nanospec is set according to a depth of the trench, which is detected in a constant frequency band corresponding to a thickness of the insulating layer. Then, a laser beam is scanned on the pattern in the shape of a lattice using a nanospec device to detect the indicated value in the desired frequency band. Then, the indicated value is calculated in terms of a thickness.
Another method for forming patterns for measuring an STI profile is disclosed in Korean Patent Registration No. 0316054. With this method, a test pattern is formed that has many bar patterns with regular width to form an isolation layer of a device to define an active region. A process is then monitored by measuring the degree of protrusion or sinking of the isolation layer of the device via detecting the difference between the width of the active region and the width of the isolation layer of the device by using Atomic Force Microscope (AFM) equipment.
Further, U.S. Pat. No. 6,350,994 discloses a structure of CD bar. The CD bar is formed on a substrate between dies. A base layer is formed on a portion of the substrate. A critical material layer is then formed on the die, the base layer and the substrate with a uniform thickness. The base layer has a thickness that provides a surface profile the same as the die. A die photomask pattern and first and a second test photomask patterns on a photomask are then transferred to the critical material on dies, the base layer, and the substrate, respectively. These three photomask patterns have the same pattern width.
Still further, U.S. Pat. No. 4,364,010 discloses a semiconductor device with a monitor pattern and a method for monitoring device parameters. The monitor pattern comprises a semiconductor layer, a first region, a second region, and a third region. The first region is formed in the semiconductor layer. The second region is formed within the first region so that the surface of the first region is divided into two portions. The third region is formed in the semiconductor layer and electrically connected to the substrate. One of the two portions of the first region is electrically connected to the third region. As the second region becomes deeper, the connection (lying beneath the second region) that connects the two portions of the first region becomes thinner. As this connection becomes thinner, its resistance is increased. Thus, monitoring of resistance between the two portions of the first region provides an index of the depth of the second region, and thereby doping profile changes during manufacture.
With the conventional methods described above, it is possible to measure CD and depth and forming a monitoring pattern of a unit device such as a transistor and a diode. However, there remains a difficulty in forming a monitoring pattern of composite devices.
As the technology of fabricating semiconductor develops, chip sizes decrease, the line width of circuits becomes thinner, and composite devices become more prevalent. Therefore, known methods of using an in-line monitoring pattern and unit device monitoring pattern will soon reach their technological limits.